Flow measurement is the production and living is for common measurement of fluid physical indicators, there are many types of the principle of flow measurement, such as ultrasonic, electromagnetic, pressure, temperature measurement principle, under normal circumstances, the flowmeter signal from the flow, pressure, temperature detecting element, the installation position of the reasonable choice of different measurement, can reduce the fluid disturbance and noise effect, improve the detection effect.
Pressure testing such flowmeter for common for orifice flow meter
, flowmeter of pig, venturi tube by the pressure testing of the throttle device, such as using diffusion silicon pressure sensor or ceramic pressure sensor.
According to the principle of vortex precession, elected in the measuring tube throat pressure hole position, because the throat pressure can represent nuclear precession vortex area of pressure.
Vortex signal detection is common spiral vortex flowmeter, turbine flowmeter, and other products, can choose heat sensitive, sensitive, capacitance, ultrasonic, optical, electromagnetic, such as detecting element, testing the vortex caused by local velocity variation and fluid pressure pulsation, realize the vortex signal detection.
The rational selection of installation position detecting element, to obtain high strength, low noise vortex signal has very good effect.
By experiment, the vortex signal detection device installed in the measuring tube section near the junction of the throat and expansion of the effect is better, the position of the vortex precession is strong, and less noise.
Adopts double detecting element detection method, has better measuring result.
In the measuring tube measurement, two symmetrical set a pair of vortex signal detecting element.
Using the phase difference of two vortex signal is 180 degrees, adopts a differential detection method, can obtain double signal, and can effectively eliminate common-mode interference, such as the pipeline vibration, flow field disturbance, etc. , so as to greatly improve the SNR, expand the flow measurement range.
Detecting element size should be small, as far as possible to reduce the detecting element flow field disturbance.
If use insert type detecting element, should consider the influence of the detecting element insertion depth of the fluid.
Detecting element size, insert depth, increases the throttling effect, flow field disturbance also increases, the stability of the precession of the vortex core and frequency may also be affected.
Tests show that insert depth increases, the flow meter coefficient K increases, but the linearity of flowmeter.
Fluid temperature detecting the temperature of the fluid is mostly adopts platinum resistance detecting element, the element stability and reliability are better, the price is not high, small volume, convenient installation.
In recent years, the emergence of diaphragm platinum resistance detecting element, small volume, fast response, is a good temperature measuring element.
Temperature measuring point location should fall within the measuring tube outlet, the fluid temperature and throat basic same, temperature measuring device will not cause interference to the vortex core precession.
Other types of electromagnetic flowmeter measurement way is the basis of the principle of electromagnetic induction, according to the conductive fluid through additional magnetic field induced electromotive force to measure an instrument of conductive fluid flow.
Another is contact flow measurement methods, typical products on behalf of the outer clamp type ultrasonic flowmeter, ultrasonic flowmeter with outer clamp is made by quantitative ultrasound from external, according to the principle of ultrasonic reflection of pipe flow is calculated value.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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